Abstract Backgrounds Prompt diagnosis of acute coronary occlusion based on electrocardiogram (ECG) are essential to decide proper treatment. However, particular ECG such as Wellens syndrome have been higlighted without obvious ST-segmen elevation which is signifies critical stenosis or occlusion of the proximal left anterior descending (LAD) artery but unfortunately is often unrecognized by physicians. Case Illustration A 51-year old male patient referred from district hospital diagnosed as five day onset STEMI with recurrent chest pain. The first ECG in there emergency room was a deep inverted T wave in anterior and lateral lead that immediate intervention approach not choosen. The typical infarct evolution in anteroseptal lead appear one day after the onset. Troponin level was significantly increased. Urgent angiography was performed in our hospital, unfortunately it resulted critical stenosis in proximal LAD with triple vessels and left main coronary artery disease. Then we consider send to surgery due to high coronary complexity (Syntax score:62) and optimize antianginal agent. Discussion In current practice, ST-segment elevation at the J-point, ≥ 1 mm in ≥ 2 adjacent leads (other than leads V2 and V3, where elevation of ≥ 2 mm in men or ≥ 1.5 mm in women is considered significant) for STEMI diagnosis. However, these general ECG criteria fail to identify the STEMI equivalents. Wellens syndrome is one of them that suggesting severe stenosis of the proximal LAD artery, which will develop into an acute anterior wall MI within a few days to weeks in 75% of untreated patients.